SWAD-Europe Newsletter, February 2004
Welcome to the second SWAD-Europe newsletter.
SWAD-Europe (Semantic Web Advanced Development in Europe) is an
EU-funded project which aims to support W3C's Semantic Web initiative
in Europe, providing targeted research, demonstrations and outreach to
ensure Semantic Web technologies move into the mainstream of networked
computing.
http://www.w3.org/2001/sw/Europe/
This newsletter is a monthly summary of work from the project and
selected Frequently Asked Questions and answers, written by a variety of
project participants.
In this issue:
News
1. W3C Technical Plenary - Semantic Web Interest Group meet
2. Semportal meets semblog
3. SWAD-Europe Demonstrates Technology at JISC Terminology Services
Workshop
FAQs
4. How can I make my thesaurus a part of the Semantic Web?
5. Why not use an RDF graph with blanks for querying RDF?
More detailed discussions on these topics are available on the project
weblog:
http://esw.w3.org/mt/esw/archives/2004_01.htmlhttp://esw.w3.org/mt/esw/
News
1. W3C Technical Plenary - Semantic Web Interest Group meet
Several members of the SWAD-Europe team were at the W3C All Groups and
Technical Plenary meeting near Cannes this week. Many W3C working groups
are meeting face to face including the new Semantic Web Best Practices
working group on Thursday and Friday. The Semantic Web Interest Group
(SWIG) met for the first two days; this is the renamed and refocussed
RDF Interest Group, chaired by Dan Brickley, who is also the director
of SWAD-Europe.
Read more:
A summary of the SWIG meeting (with links to logs and urls) is available
here: http://esw.w3.org/mt/esw/archives/000044.html
Kendall Clark also wrote about the meeting on xml.com:
http://www.xml.com/pub/a/2004/03/03/deviant.html
SWIG proposed charter:
http://www.w3.org/2003/12/swa/swig-charter
Semantic-Web Best Practices and Deployment (SWBPD) Working Group
Kick-off meeting agenda (with links to logs and decisions):
http://www.w3.org/2004/03/04-SWBPD
2. Semportal meets semblog
This is a brief update on our demonstrator activity on semantic portals.
As we blogged last month, we have been putting together a portal
interface tool that allows us to take a collection of RDF, in our case
descriptions of environmental organizations, and render it in a faceted
browser. This is working well and enabled us to demonstrate a prototype
successfully to Anthony Perret of the environment council at a recent
meeting.
The dimensions to use to drive the browsing are described in the form of
either RDFS class hiearchies or SKOS thesauri. It proved to be quite
easy to use Jena's rule processing engine to add rules to propagate the
transitive closure of the SKOS term lattice along with basic RDFS
processing and a little OWL support (we needed inverse properties). In
the portal description (in RDF of course) you can just specify a set of
data sources and ontologies, together with what rule file you want to
use for processing. Surprisingly simple rules have been enough to
implement the functionality needed for the demo so far.
We've also been able to connect the two tools together. For an internal
demonstration we were able to capture and classify some information
snippets in a semblog and view them in the appropriate categories in a
portal along with some preclassified documents. What makes it really fun
is that the classification scheme itself, since it's expressed in RDF,
is just another object you can browse and manipulate. So you can link in
another data source, which uses a different classification scheme, and
can see that scheme as another dimension available for use in browsing.
Read more:
A personal take on the meeting from Steve Cayzer:
http://jena.hpl.hp.com:3030/blojsom-hp/blog/news/swade/?permalink=CB93C608E80CF1F2A86DD6ADF47B67A0.textile&smm=y
SWAD-E Semantic Portals requirements specification:
http://www.w3.org/2001/sw/Europe/reports/requirements-demo-2/
3. SWAD-Europe Demonstrates Technology at JISC Terminology Services
Workshop
On Friday 13th February Libby Miller from ILRT and Alistair Miles
from CCLRC attended the JISC Terminology Services Workshop in London.
The workshop was being held to explore all issues surrounding the need
for making terminologies (thesauri, taxonomies, classification systems
etc.) available via services on the web to a wider community, and the
potential role of JISC in that effort. The Thesaurus Activity of the
SWAD-Europe project is concerned with exactly this problem, and although
our work on a thesaurus web-service API is still in progress, we've
already done some interesting pre-prototype implementations of modular
services and applications. This workshop was a chance for us to show off
our prototypes, and discuss future directions with a well-informed and
experienced group of people.
One very encouraging sign was that 'the semantic web' 'RDF' and 'OWL'
are no longer dirty words, but are more and more being considered as
viable and realistic approaches to solving these technological and
architectural problems. It is also clear that if this community is
going to start moving towards semantic web style solutions, then there
is a bridge to be built between traditional approaches to structured
vocabularies and the Web Ontology Language. The SKOS schemas may be
abler to play a significant role in building that bridge, and provide
an opportunity for the large communities of library and information
scientists to enrich the framework of the Semantic Web.
There was also some very positive feedback on the recent SKOS work,
including the reports on representing monolingual thesauri, multilingual
thesauri and inter-thesaurus mappings.
Read more on the weblog:
http://esw.w3.org/mt/esw/archives/000041.html
Frequently Asked Questions
4. How can I make my thesaurus a part of the Semantic Web?
A: To make a thesaurus a part of the semantic web, simply
* encode the thesaurus as RDF using the SKOS schemas,
* publish the RDF data.
The SKOS schemas are RDF schemas for encoding thesauri and similar types
of knowledge organisation system (KOS).
SKOS-Core is the core schema, allowing representation of thesaurus
concepts, terms, and organisation of those concepts into hierarchical
and associative structures. It has been designed as an extensible
framework of properties, and so can be adapted to cope with different
types of thesaurus.
The version of SKOS-Core currently available is a pre-release. A formal
release (version 1.0) is planned shortly, along with a guide to using
it.
SKOS-Mapping is an RDF schema for creating and encoding mappings between
thesauri. If mappings between thesauri are available, independent but
overlapping thesauri can be used interchangeably, helping to remove the
boundaries between collections and communities. A good introduction to
SKOS-Mapping with examples is here.
SKOS-Mapping is also currently available as a pre-release version. A
formal release can be expected shortly after SKOS-Core 1.0.
There are also a number of reports on issues relating to the use of
thesauri on the semantic web, including a review of previous work and a
report on multilingual thesauri. The work is ongoing, and discussed on
the public-esw-thes@w3.org mailing list (archives) - feel free to join
in!
Read more:
SKOS-Core: http://www.w3c.rl.ac.uk/SWAD/rdfthes.html#schemas
Using SKOS-Core schema: http://www.w3c.rl.ac.uk/SWAD/deliverables/8.1.html
SKOS-mapping schema: http://www.w3c.rl.ac.uk/SWAD/rdfthes.html#schemas
SKOS-Mapping examples: http://www.w3c.rl.ac.uk/SWAD/deliverables/8.4.html
Thesaurus reports: http://www.w3c.rl.ac.uk/SWAD/rdfthes.html#reports
Thesaurus mailing list archives: http://lists.w3.org/Archives/Public/public-esw-thes/
5. Why not use an RDF graph with blanks for querying RDF?
A. You can, some people have, it can be useful but is much less
expressive than most full RDF query languages.
In RDF, blank notes are treated as existential variables - they indicate
the existence of a thing without saying anything about the name of that
thing. So it is reasonable to express a query as a graph with bNodes
used as if they were wildcards and to define a query operation as
something like "find all instances of the query graph which are entailed
by the data". Perhaps, your operation might want to the find the union
of that set of matching subgraphs rather than return the separate
matches, depending on the application.
This can work but it is quite restrictive.
First, bNodes can only be used in place of nodes, not in place of
properties. This is a big limitation since many queries require matching
over properties. Second, you can't express constraints such as string
pattern matches or range constraints on the literals to be matched. To
get around this, attempts at this "query by example" approach often use
metalevel annotations to allow such things to be expressed. For example,
see our own experiments this area, RDF-QBE. Once, you start doing this
you can use the annotations to identify the query nodes in the first
place and not bother using bNodes at all. This is essentially, what the
simplest of the Edutella query languages, RDF-QEL-1, does.
Other limitations are the inability to express disjunctive queries this
way (RDF is purely conjunctive) and the akwardness of expressing
constraints between variables.
Despite these limitations the symmetry of expressing queries, and indeed
the resulting matches, directly in RDF rather than indirectly encoded in
RDF is appealing and could be appropriate in some applications.
Read more:
RDF-QBE: http://www.hpl.hp.com/semweb/publications.htm#RDF-QBE
Edutella: http://edutella.jxta.org/reports/edutella-whitepaper.pdf
Visit the SWAD-Europe website:
http://www.w3.org/2001/sw/Europe/http://www.w3.org/2001/sw/Europe/reports/intro.html
and weblog:
http://esw.w3.org/mt/esw/
for ongoing information about the project.